There has been a trend to provide radio frequency (RF) systems which are compatible with radar, communications and/or electronic warfare (EW) systems. RF systems which are compatible with radar, communications and/or EW systems are sometimes referred to as multifunction systems. Each of the radar, communications and EW systems typically operate in different RF frequency bands. Thus, multifunction systems often include a wide band antenna (typically an array antenna) which is responsive to RF signals over a wide range of RF frequencies such that RF signals in the radar, communications and EW frequency ranges can be received by the antenna.
Multifunction systems may also include multiple RF receivers, with different ones of the receivers tuned to receive signals in one of the radar, communications or EW frequency bands. Each of the RF receivers thus has a bandwidth which is less than the overall bandwidth of the wide band antenna. It is thus necessary to separate or “channelize” the broadband RF signals received by the antenna into portions appropriate for reception by respective ones of the narrow band receivers. Once the RF signals are separated (or channelized) into desired RF bands, the output signals of those bands can be provided to the appropriate ones of the narrow band receivers.
Typically, a multi-stage channelizer, (also referred to herein as an “N-channel multiplexer” or more simply, an “N-plexer”), is used to separate RF signals. A multi-stage channelizer splits an input signal having a frequency bandwidth into N signals each having a subset of the frequency bandwidth. For example, a one-stage channelizer (also referred to herein as a two-channel multiplexer) may split an input signal operating over a 10 to 20 GHz bandwidth into a first signal having a first bandwidth (e.g. a 10 to 12 GHz bandwidth) and a second signal having a second bandwidth (e.g. a 12 to 20 GHz bandwidth).
One technique to channelize broadband signals is to use a channelizer which includes an active tunable filter. This technique requires DC power to be provided to the channelizer for the active tunable filter and also requires a relatively complex filter. Passive techniques include the use of Wilkinson power dividers. Passive techniques are relatively simple to implement, however, such techniques also add 3 dB of insertion loss for each desired channel. N-stage channelizers may also be constructed from baluns. However, prior attempts to construct N-stage channelizers using baluns have focused on double-y baluns or three-port baluns.